The present invention relates to an X-ray image radiographing method and an X-ray image radiographing apparatus, and specifically to an X-ray image radiographing method and an X-ray image radiographing apparatus in which, when an X-ray tube to radiate the divergent X-ray is used and the magnifying radiography is conducted, the X-ray image having the excellent sharpness is obtained by the edge enhancement by the X-ray refraction contrast.
The X-ray image using an action in which the X-ray transmits the substance, is widely used for the medical image diagnosis and non-destructive inspection. This X-ray image is a shade and shadow image obtained from a fact that, when the X-ray transmits an object, an X-ray transmission amount is different depending on the value of the atomic weight of the substance constituting the object. That is, the two-dimensional distribution of the X-ray intensity which is radiated from the X-ray source and which transmits through the object, is detected by an X-ray image detector, and the X-ray image based on the X-ray absorption contrast of the object is formed.
As an example of the X-ray tube which radiates the divergent X-ray used for the non-destructive inspection and in the general medical facility, there is a rotational anode X-ray tube, and in this X-ray tube, the X-ray generated when a thermoelectron collides with an anticathode spreads radially. By using this characteristic, by keeping the distance between the object and the X-ray image detector apart, the magnifying radiography of the X-ray image is conducted. At this time, because a size of focal spot of the X-ray is a finite value, it is well known that, in the magnifying radiography, as shown in FIG. 1, blurs called xe2x80x9cpenumbraxe2x80x9d are generated.
When the X-ray source is a point light source, or when the X-ray source can be regarded as a point light source, that is, when the size of focal spot is 0, or almost 0, blurs are not generated in the X-ray image of such the magnifying radiography. On the one hand, when the sufficient X-ray intensity to transmit through the thick object such as a human body is tried to have, practically, a finite value of size of focal spot is necessary. Accordingly, in the Radiography, blurs due to this penumbra can not be avoided, and specifically, in the case of the magnifying radiography, the sharpness of the X-ray image is decreased.
Then, when the magnifying ratio of the magnifying radiography is increased, the width of the blur is further enlarged. For example, in the magnifying radiography such as the chest spot radiography, or the born portion accurate radiographing, when its magnifying ratio is increased, the sharpness of the image is deteriorated, therefore, radiographing becomes rather difficult, and the effect of the magnifying radiography is decreased to half.
On the one hand, the present inventors find that, when the object is radiographed, the edge enhancement phenomenon by the refraction contrast of the X-ray is generated at a portion having the refractive index of the object.
The present invention is attained in view of the foregoing problems, and its object is to provide an X-ray image radiographing method by which, when the magnifying radiography is conducted by using an X-ray tube which radiates divergent X-ray, by optimizing the relationship between the blur due to the penumbra and the edge enhancement, the magnifying radiographic image having the excellent sharpness can be obtained, and a radiographing apparatus using the method.
In order to solve the above problems and to attain the object, the present invention is structured as follows.
(1) An X-ray image radiographing method in which an X-ray tube to radiate a divergent X-ray is used, and the X-ray radiated from the X-ray tube is made to transmit the object and the magnifying radiography is conducted, and when the width of the blur due to the penumbra of the X-ray image obtained by the magnifying radiography is B (xcexcm), and the width of the edge enhancement by the X-ray refraction contrast is E (xcexcm), 9 Exe2x89xa7B.
(2) The radiographing method according to (1), wherein the magnifying ratio of the magnifying radiography is 1.1-10 times.
(3) The radiographing method according to (1) or (2), wherein the size of focal spot of the X-ray tube is 0.03 mm-0.3 mm.
(4) The radiographing method according to any one of (1) to (3), wherein the X-ray tube voltage of the X-ray tube is 50 kVp-150 kVp.
(5) The radiographing method according to any one of (1) to (4), wherein the X-ray tube is a Coolidge X-ray tube.
(6) The radiographing method according to any one of (1) to (5), wherein the X-ray tube is a tungsten rotational anode X-ray tube.
(7) The radiographing method according to any one of (1) to (6), wherein a screen film system whose average gradient G is 1.5-4.0 is used, and the edge enhancement width E is not smaller than 9 xcexcm.
(8) The radiographing method according to any one of (1) to (7), wherein a digital X-ray image detector whose pixel size is 1 xcexcm-200 xcexcm, is used, and the edge enhancement width E is not smaller than 0.1 xcexcm.
(9) The radiographing method according to any one of (1) to (8), wherein the object is a human body or a medical sample taken out from the human body.
(10) An X-ray image radiographing apparatus, which having: the X-ray tube to radiate the divergent X-ray; an object position setting tool to set a position of the object to the X-ray tube; and the X-ray image detector to detect the X-ray image transmitted through the object, wherein, when the blur width due to the penumbra of the X-ray image is B (xcexcm), and the edge enhancement width due to the X-ray refraction contrast is E (xcexcm), and when the X-ray radiated from the X-ray tube is made to transmit the object and the magnifying radiography is conducted, the object position setting tool and the X-ray image detector can be arranged so that 9 Exe2x89xa7B.
(11) The X-ray image radiographing apparatus according to (10), wherein the object position setting tool can be provided so that the distance between the X-ray tube and the object is apart not smaller than 0.5 m, and the distance from the object to the X-ray image detector can be apart not smaller than 1 m.
(12) The X-ray image radiographing apparatus according to (11), wherein the apparatus has a rail or a support provided with the information of the distance with the focus of the X-ray tube as the start point, and a holder for the X-ray image detector to hold the X-ray image detector, and wherein the object position setting tool and the holder for the X-ray image detector are provided on the rail or the support so that these can be moved and can temporarily be fixed.
(13) The X-ray image radiographing apparatus according to any one of (10)-(12), wherein the apparatus has the X-ray tube in which the tube voltage of 50 kVp-150 kVp can be set, and the object position setting tool is located at a position apart from the X-ray tube by not smaller than 0.5 m, and the X-ray image detector is located at a position apart from the object position setting tool by not smaller than 1 m.
(14) The X-ray image radiographing apparatus according to (10) to (13), wherein the magnifying ratio of the magnifying radiography is 1.1-10 times.
(15) The X-ray image radiographing apparatus according to any one of (10) to (14), wherein the size of focal spot of the X-ray tube is 0.03 mm-0.3 mm.
(16) The X-ray image radiographing apparatus according to any one of (10) to (15), wherein the X-ray tube is a Coolidge X-ray tube.
(17) The X-ray image radiographing apparatus according to any one of (10) to (16), wherein the X-ray tube is a tungsten rotational anode X-ray tube.
(18) The X-ray image radiographing apparatus according to any one of (10) to (17), wherein a screen film system whose average gradient G is 1.5-4.0 is used as the X-ray image detector, and the edge enhancement width E is not smaller than 9 xcexcm.
(19) The X-ray image radiographing apparatus according to any one of (10) to (18), wherein the digital X-ray image detector whose pixel size is 1 xcexcm-200 xcexcm is used as the X-ray smaller than 0.1 xcexcm.